Antennas present considerable mechanical packaging challenges. To place an antenna in a confined space with electronics may lead to sacrifices in antenna efficiency, frequency of operation, percentage bandwidth or other characteristics.
Dipole-type antennas are affected by the mechanical design of the chassis and electronics. Dipole antennas require physical separation between the antenna and any conductive metal, including the electronics on a printed circuit board. To space the antenna away from the chassis and electronics, a cable is typically used and the antenna is mounted on the non-metal packaging. Cables and separated antennas drive the size of the packaging larger and the cost of the antenna solution higher.
Inverted F antennas (IFA) and monopole antennas may be implemented in a printed circuit board. However, IFA and monopole antennas require a reserved area for the antenna to be isolated from the electronics of the printed circuit board. This drives up the size and cost of the printed circuit board and packaging.
Planar inverted F antennas (PIFA) may be implemented in several ways. Normally, PIFA are formed from thin metal, which is cut and bent precisely for operation at the desired frequency. Usually this type of antenna requires a cable for connection between the folded metal structure and transceiver circuit. For lower frequency operation, a larger area is needed since antenna size increases inversely with frequency. Thus, Bent-Metal PIFAs may be limited to frequencies above 2 GHz. At 2 GHz, the folded metal length is about 1.5 inches. In high volume small electronic products, folded metal antennas are problematic above that size. Folded metal and associated cables drive up the size and cost of the packaging.
PIFA antennas may also be implemented by using the top and bottom layers of a printed circuit board. Separate metal structures are formed in different layers of the printed circuit board to realize the PIFA. To provide the isolation from the electronic circuitry, a reserved area of the printed circuit board is used. But since the printed circuit board material is between the metal structures, the PCB-based PIFA suffers from poor efficiency due to the poor dielectric loss of the board material. The small thickness (e.g., 0.059 mils) also results in an extremely narrow bandwidth for the PIFA. Thus, the PCB-based PIFA is rarely used in practice.